This CDK Construct allows users to add and update origins and behaviors on an existing Cloudfront Distribution. This is specifically useful if you manage a Distribution through a separate CDK Stack and must import it into the Stack for one of your applications.
This Construct works by calling the Cloudfront API through a CustomResource and makes no attempt to avoid destructive updates. It reads the existing Cloudfront Distribution config and updates it with the provided origin and behavior. If the origin or behavior are already present on the Distribution, it will overwrite them. Origins are identified by their Id property and Behaviors are identified by their PathPattern property. If you provide an Origin with an Id that already exists on the Distribution, the existing Origin with that Id will be overwritten. If you provide a Behavior with a PathPattern that already exists on the Distribution, the existing Behavior with that PathPattern will be overwritten.
The flipside of this is the Construct does not touch any configuration in the Distribution that does not collide with the provided Origin or Behavior (on the assumption that you may be adding additional Origins and Behaviors in other Stacks). A side effect of this is if you run this Construct with a specific Origin Id and later change the Id, a new Origin will be created, but the previous Origin will not be deleted. You will need to manually delete the old Origin.
from constructs import Construct
from cdk_cloudfront_update.constructs import CloudfrontUpdate
class MyApi(Construct):
def __init__(
self,
scope: Construct,
id: str,
distribution_arn: str,
service_path_pattern: str,
load_balancer_dns_name: str,
**kwargs,
):
"""
Add MyAPI service to the Cloudfront Distribution at the
specified path.
"""
super().__init__(scope, id, **kwargs)
origin_id = "ApiLoadBalancer"
CloudfrontUpdate(
self,
"my-api-cf-update",
distribution_arn=distribution_arn,
behavior_config={
"PathPattern": service_path_pattern,
"TargetOriginId": origin_id,
"TrustedSigners": {"Enabled": False, "Quantity": 0},
"TrustedKeyGroups": {"Enabled": False, "Quantity": 0},
"ViewerProtocolPolicy": "redirect-to-https",
"AllowedMethods": {
"Quantity": 7,
"Items": [
"HEAD",
"DELETE",
"POST",
"GET",
"OPTIONS",
"PUT",
"PATCH",
],
"CachedMethods": {"Quantity": 2, "Items": ["HEAD", "GET"]},
},
"SmoothStreaming": False,
"Compress": True,
"LambdaFunctionAssociations": {"Quantity": 0},
"FunctionAssociations": {"Quantity": 0},
"FieldLevelEncryptionId": "",
"CachePolicyId": "4135ea2d-6df8-44a3-9df3-4b5a84be39ad", # Managed CachingDisabled Policy
"OriginRequestPolicyId": "216adef6-5c7f-47e4-b989-5492eafa07d3", # Managed AllViewer Origin Request Policy
},
origin_config={
"Id": origin_id,
"DomainName": load_balancer_dns_name,
"OriginPath": "",
"CustomHeaders": {"Quantity": 0},
"CustomOriginConfig": {
"HTTPPort": 80,
"HTTPSPort": 443,
"OriginProtocolPolicy": "http-only",
"OriginSslProtocols": {"Quantity": 1, "Items": ["TLSv1.2"]},
"OriginReadTimeout": 60,
"OriginKeepaliveTimeout": 5,
},
"ConnectionAttempts": 3,
"ConnectionTimeout": 10,
"OriginShield": {"Enabled": False},
},
)This Construct makes use of the Cloudfront API's update-distribution, so values for behavior_config and origin_config can be derived from the API docs for CacheBehavior and Origin.
By default, the Construct will create a Lambda function with permission to Get and Update the specified Distribution. In some cases, you may need to grant it additional permissions. For example, if you want to add a Lambda@Edge function to the CacheBehavior, you will need to grant additional Lambda permissions in order for the API call to succeed. For example:
from aws_cdk import aws_lambda
from constructs import Construct
from cdk_cloudfront_update.constructs import CloudfrontUpdate
class MyApi(Construct):
def __init__(
self,
scope: Construct,
id: str,
distribution_arn: str,
service_path_pattern: str,
load_balancer_dns_name: str,
**kwargs,
):
"""
Add MyAPI service to the Cloudfront Distribution at the
specified path.
"""
super().__init__(scope, id, **kwargs)
# Create a Lambda Function for use with Lambda@Edge
edge_fn_role = iam.Role(
self,
"EdgeFnRole",
assumed_by=iam.CompositePrincipal(
iam.ServicePrincipal("edgelambda.amazonaws.com"),
iam.ServicePrincipal("lambda.amazonaws.com"),
),
)
edge_fn = aws_lambda.Function(
self,
"EdgeFn",
handler="main.handler",
role=thumbnail_role,
code=aws_lambda.Code.from_asset(
os.path.join(
os.path.dirname(__file__),
"edge_lambda_src",
)
),
runtime=aws_lambda.Runtime.PYTHON_3_8,
timeout=Duration.seconds(5),
)
cf_update_policy = iam.PolicyStatement(
effect=iam.Effect.ALLOW,
actions=[
"lambda:GetFunction",
"lambda:EnableReplication*",
],
resources=[edge_fn.current_version.function_arn],
)
origin_id = "ApiLoadBalancer"
CloudfrontUpdate(
self,
"my-api-cf-update",
distribution_arn=distribution_arn,
lambda_execution_policy_statements=[associate_policy],
behavior_config={
...
"LambdaFunctionAssociations": {
"Quantity": 1,
"Items": [
{
"LambdaFunctionARN": edge_fn.current_version.function_arn,
"EventType": "viewer-request",
"IncludeBody": False,
},
],
},
},
origin_config={
...
},
)You may need multiple instances of this Construct within the same Stack. If so, you will need to define a dependency between the CustomResource for each instance, such that they trigger sequentially and avoid collisions when calling the API. For example:
api_cf = CloudfrontUpdate(
self,
"my-api-cf-update",
...
)
static_site_cf = CloudfrontUpdate(
self,
"my-static-site-cf-update",
...
)
static_site_cf.resource.node.add_dependency(api_cf.resource)In order to support the latest version of the Cloudfront API, this Construct will build a Lambda Layer including the latest version of boto3. This requires Docker to be running and will store the layer files in ./cdk.out/layers/cf_update_deps_layer.
In the event that it is desirable for the custom resource to run at every deployment, a nonce argument can be provided to the construct. This will trigger the redeployment of the CustomResource but not the Lambda or related IAM policies.
from time import time
from constructs import Construct
from cdk_cloudfront_update.constructs import CloudfrontUpdate
class MyApi(Construct):
def __init__(
self,
scope: Construct,
id: str,
distribution_arn: str,
service_path_pattern: str,
load_balancer_dns_name: str,
**kwargs,
):
"""
Add MyAPI service to the Cloudfront Distribution at the
specified path.
"""
super().__init__(scope, id, **kwargs)
origin_id = "ApiLoadBalancer"
CloudfrontUpdate(
self,
"my-api-cf-update",
distribution_arn=distribution_arn,
behavior_config={
"PathPattern": service_path_pattern,
"TargetOriginId": origin_id,
"TrustedSigners": {"Enabled": False, "Quantity": 0},
"TrustedKeyGroups": {"Enabled": False, "Quantity": 0},
"ViewerProtocolPolicy": "redirect-to-https",
"AllowedMethods": {
"Quantity": 7,
"Items": [
"HEAD",
"DELETE",
"POST",
"GET",
"OPTIONS",
"PUT",
"PATCH",
],
"CachedMethods": {"Quantity": 2, "Items": ["HEAD", "GET"]},
},
"SmoothStreaming": False,
"Compress": True,
"LambdaFunctionAssociations": {"Quantity": 0},
"FunctionAssociations": {"Quantity": 0},
"FieldLevelEncryptionId": "",
"CachePolicyId": "4135ea2d-6df8-44a3-9df3-4b5a84be39ad", # Managed CachingDisabled Policy
"OriginRequestPolicyId": "216adef6-5c7f-47e4-b989-5492eafa07d3", # Managed AllViewer Origin Request Policy
},
nonce=str(time())
)